Pistons which are adapted for use in hydraulic pumps and motors are subject to significant stress levels and high velocities, as the pistons translate and rotate within a cylinder block. In order to withstand such a harsh operating environment, they should be constructed from a strong wear resistant material, but simultaneously not hinder performance with excess weight. Therefore, a hollowed section may be provided in the piston, as disclosed by Havens in U.S. Pat. No. 3,319,575, for example.
However, often in the construction of pistons with hollowed sections, excess particles from the process of joining the various segments together may settle within the hollowed section. This poses a significant problem as the undesirable particles wear on the inner walls of the piston during operation within the cylinder block, and subsequently contaminate the piston structure. Continual translational and rotational motion may trigger failure of one of the pistons, and eventually cause malfunctioning of the hydraulic unit.
The problems of weld particles within a piston chamber used in internal combustion engines is recognized in a patent to Kohl et al., U.S. Pat. No. 3,319,536. Kohl et al. discloses the use of annular rings spaced from the piston chamber into which the ends of charged particle beams extend, so that if the welded seams created from the charged particle beams tear, the tear will follow the contour of the rings. While Kohl et al. seeks to overcome the problem of excess weld particles by providing a extrinsic element, it does not, as the invention to be described more fully hereinafter, teach providing a circumferentially extending recessed area within the piston structure to receive and contain particles produced while constructing the piston.
The present invention is directed to overcoming the above-referenced problems.